New Precision Measurement of Hyperfine Splitting of Positronium

Abstract

The ground state hyperfine splitting of positronium ∆ HFS is sensitive to high order corrections of quantum electrodynamics (QED) in bound state. The theoretical prediction and the averaged experimental value for ∆ HFS has a discrepancy of 15 ppm, which is equivalent to 3.9 standard deviations (s.d.). A new precision measurement which reduces the systematic uncertainty from the positronium thermalization effect was performed, in which the non-thermalization effect was measured to be as large as 10 ± 2 ppm in a timing window we used. When this effect is taken into account, our new result becomes ∆ HFS = 203.394 2 ± 0.001 6(stat., 8.0 ppm) ± 0.001 3(sys., 6.4 ppm) GHz, which favors the QED prediction within 1.2 s.d. and disfavors the previous experimental average by 2.6 s.d.

Search for New Physics with Atoms and Molecules

“…Improvements in precision are required to resolve this discrepancy. [A more recent experiment does claim to have a result closer to theory (Ishida, 2015;Ishida et al, 2014)]. There are suggestions about beyond SM physics mechanisms to which positronium might be particularly susceptible (Lamm, 2017), and there are substantial efforts to extend QED theory to order α 7 in order to sharpen the comparison with experiment (Adkins et al, 2015;Eides and Shelyuto, 2017).…”